I've used four different CD rings including a green and black Marigo. The Herbie's use results are the same in my system as in Robert and Frank's. Diminished musicality, reduced dynamics and compressed sound. Not good. However, I have an alternative use for the black hole. I use it around the center spindle of my VPI TNT VI with superplatter. It slightly lifts the label area to good effect with the VPI heavyweight to provide a better VTA for standard LPs (140mm and thinner). It's probably due to the VPI platter's slight indentation slope towards the spindle area.
I also have an Ultradesk cutter and demagnetizer. I have since found that the Walker Talisman demagnetizer to be a superior and elegant product to use on every disc, CD and LP, with obvious benefit to every CD I play. Sure, it over $200 for a pair of magnets but I use it exclusively since 2008. Wonderful product or make your own. Easy to test. Play an undemagnetized CD, then swipe the Talisman on top and below the tray with the disc in it holding a finger on the edge. Then replay CD. Voila, clearer, cleaner sound. Just as if the resolution increased and distortion/hashy sound decreased. I wouldn't want to be without it.
I also highly recommend Herbie's tube dampers. I've also used dual silicone rings around tubes to lessen tube vibration to great affect. Tube vibration is not a good thing for audio. Many cheap current production tubes can be made so much better sounding with just adding vibration control. E.g. EAR 864 phono stage has EJ 12AX7s. Placing dual silicone rings on each tube will improve the sound of those tubes 100%, closer to a nice pair of NOS Siemans or Philips (not as good, but a lot closer). Luckily my phono pre and pre-amp have only subminiature tubes with nearly vibration free glass envelopes (suitable for bomb use).
I also have an Ultradesk cutter and demagnetizer. I have since found that the Walker Talisman demagnetizer to be a superior and elegant product to use on every disc, CD and LP, with obvious benefit to every CD I play. Sure, it over $200 for a pair of magnets but I use it exclusively since 2008. Wonderful product or make your own. Easy to test. Play an undemagnetized CD, then swipe the Talisman on top and below the tray with the disc in it holding a finger on the edge. Then replay CD. Voila, clearer, cleaner sound. Just as if the resolution increased and distortion/hashy sound decreased. I wouldn't want to be without it.
I also highly recommend Herbie's tube dampers. I've also used dual silicone rings around tubes to lessen tube vibration to great affect. Tube vibration is not a good thing for audio. Many cheap current production tubes can be made so much better sounding with just adding vibration control. E.g. EAR 864 phono stage has EJ 12AX7s. Placing dual silicone rings on each tube will improve the sound of those tubes 100%, closer to a nice pair of NOS Siemans or Philips (not as good, but a lot closer). Luckily my phono pre and pre-amp have only subminiature tubes with nearly vibration free glass envelopes (suitable for bomb use).